Ross Levinsohn, who was interim chief executive officer of Yahoo! until Marissa Mayer became CEO in July, said his successor will need years and a patient board to turn around the Web portal.

“You have to give Marissa and the team that’s there the time to finish the job,” Levinsohn said. “You can’t turn that company or any company of size around in six months or a year.”

Levinsohn held the top post at Yahoo! less than three months, and had become a candidate to lead the company before the unexpected hiring of Mayer, an executive from Google. The new CEO, Yahoo’s fifth in three years, is seeking to reverse three years of declining revenue at the biggest US Web portal.

Mayer is one of several execs attempting to revive a struggling technology icon, including Meg Whitman at Hewlett-Packard and Tim Armstrong at AOL.

“Yahoo! is a battleship,” Levinsohn said. “To turn a battleship takes a long time, but once you turn that battleship the right way, it’s a battleship, and it can really inflict some damage.”

Yahoo! is targeting growth in online search, display advertising, mobile applications and products such as e-mail, Mayer said earlier this month.

She may find it hard to grow e-mail, which does not attract many new users, Levinsohn said.